Warlocks in a party with a healer can boost their mana if the healer agrees. Note that the self-inflicted damage will rank low on the healers priority list - after the tank and party members taking aggro.

Between fights, use Life Tap to bring your life and mana even. This way, you will regenerate both hp and mana at the same time, and will decrease your downtime.

While Life Tap will allow you to continue casting, it does trigger your GCD, reducing your overall DPS, and should be used sparingly.